The apparatus for receiving BS digital broadcast for receiving the BS (Broadcasting Satellite) digital broadcast receives a signal transmitted by the time sharing by using a plurality of modulation techniques of multi-phase PSK modulations such as 8 PSK (Phase Shift Keying) modulation, QPSK (Quadrature PSK) modulation, or BPSK (Binary PSK) modulation in the way of time sharing. The apparatus for receiving BS digital broadcast regenerates the carrier by detecting the phase error of the received signal, and demodulates the digital signal.
Conventionally, the apparatus for receiving BS digital broadcast which regenerates the carrier by using a single demodulator circuit switches the receiving operation according to the magnitude of the CNR in the received signal. For example, when the CNR is large (at the time of a high CNR), it performs continuous receiving while responding all modulation techniques, and detects the phase error and regenerates the carrier. On the other hand, when the CNR is approximately in the middle degree (at the time of a medium CNR), it performs burst receiving of a signal subjected to the QPSK modulation and a signal subjected to the BPSK modulation and detects the phase error, and regenerates the carrier. Furthermore, when the CNR is small (at the time of a low CNR), it performs burst receiving of a signal subjected to the BPS modulation and detects the phase error, ad regenerates the carrier.
FIG. 3 is a drawing indicating one example of the structure of such a conventional apparatus for receiving BS digital broadcast.
Here, when performing the burst receiving of a signal, for example, such an operation of holding the output of a loop filter 106 during the term when a signal which cannot detect the phase error arrives is performed.
Furthermore, The apparatus for receiving BS digital broadcast switches the receiving operation according to a switching instruction signal generated by a decoding section 109.
The decoding section 109 monitors the error rate or the like after performing the trellis decoding or the like (Viterbi decoding in the case of QPSK or BPSK), and when the error rate or the like becomes a previously determined value, it generates a switching instruction signal for instructing the switching of the receiving operation.